1. Field of the Invention
The present invention relates to an electroacoustic transducer which generates a sound by means of electromagnetic acoustic conversion.
2. Description of the Related Art
An electroacoustic transducer has a magnetic circuit in which a magnetic field from a magnet passes through a base member, a magnetic core and a diaphragm, and returns to the magnet again. When an electric oscillating signal is supplied to a coil disposed around the magnetic core, an oscillating magnetic field generated by the coil is superimposed on the magnetostatic field of the magnetic circuit so that oscillation generated in the diaphragm is transmitted to air. Thus, sound is generated.
The electroacoustic transducer is provided with terminals for supplying a current to a coil, and the terminals are often connected to a wiring pattern of a circuit board by soldering or the like in the same manner as other electronic parts.
Methods for winding the coil so as to mount the coil on the surrounding of the magnetic core are roughly classified into a) a direct winding method in which a coil wire is wound around a coil bobbin after the coil bobbin is fitted to the magnetic core, and b) a separate winding method in which a coil wire is wound around a reusable coil bobbin, the shape of the coil is fixed by bonding or the like, and thereafter the coil is taken out from the coil bobbin and mounted on a transducer.
The separate winding method is superior in mass productivity of coil. However, when a coil is mounted on a transducer, a lead wire of the coil is extremely thin so that caution is required in coil terminal treatment for connecting the lead wire to terminals. This caution becomes the bottleneck for the improvement of the productivity.
On the other hand, the direct winding method indeed has an advantage that coil winding and coil terminal treatment can be carried out simultaneously. However, a coil bobbin is required so that the number of parts or the number of man-hour for assembling increases.
It is an object of the present invention to provide an electroacoustic transducer in which the number of parts and the manufacturing cost can be prevented from increasing, and the assembling strength and the reliability of the electroacoustic transducer can be improved.
According to the present invention, there is provided an electroacoustic transducer comprising: a base member made of magnetic material; a magnetic core made of magnetic material and provided erectly on the base member; a diaphragm made of magnetic material and supported with a gap between the diaphragm and a forward end of the magnetic core; a magnet constituting a magnetic circuit together with the base member, the magnetic core and the diaphragm so as to provide a magnetostatic field; a coil disposed around the magnetic core for applying an oscillating magnetic field to the magnetic circuit; a coil bobbin interposed between the magnetic core and the coil for holding the coil; and a housing member for receiving the base member, the magnetic core, the diaphragm, the magnet, the coil and the coil bobbin; wherein the coil bobbin is molded integrally with the magnetic core and the base member.
According to the present invention, the coil bobbin is molded integrally with the magnetic core and the base member by insert molding or the like. Thus, it is not necessary to bond the coil bobbin. It is therefore possible to improve the fixation strength of the coil bobbin to the magnetic core and the base member and it is possible to reduce the number of parts and the manufacturing cost.
Further, according to the present invention, there is provided an electroacoustic transducer comprising: a base member made of magnetic material; a magnetic core made of magnetic material and provided erectly on the base member; a diaphragm made of magnetic material and supported with a gap between the diaphragm and a forward end of the magnetic core; a magnet constituting a magnetic circuit together with the base member, the magnetic core and the diaphragm so as to provide a magnetostatic field; a coil disposed around the magnetic core for applying an oscillating magnetic field to the magnetic circuit; a housing member for receiving the base member, the magnetic core, the diaphragm, the magnet and the coil; terminals for supplying an electric current from the outside to the coil; and an electrically insulating member for electrically insulating the base member from the terminals; wherein the electrically insulating member is molded integrally with the base member.
According to the present invention, the electrically insulating member for electrically insulating the base member from the terminals is molded integrally with the base member by insert molding or the like. Thus, it is not necessary to bond the electrically insulating member. It is therefore possible to improve the fixation strength of the electrically insulating member to the base member and it is possible to reduce the number of parts and the manufacturing cost.
Further, according to the present invention, preferably, the electrically insulating member is molded integrally with the terminals.
According to the present invention, the electrically insulating member is molded integrally not only with the base member but also with the terminals by insert molding or the like. Thus, it is not necessary to bond the terminals. It is therefore possible to improve the fixation strength of the terminals and it is possible to reduce the number of parts and the manufacturing cost.
Further, according to the present invention, preferably, an external surface of the base member is covered with the electrically insulating member.
According to the present invention, when the base member and the electrically insulating member are molded integrally by insert molding or the like, the external surface of the base member is covered with the electrically insulating member. Thus, the quantity of a sealer to be used for sealing the bottom surface of the transducer can be reduced largely. In addition, the base member is not exposed to the outside. Thus, the base member can be prevented from short-circuit, dew condensation, or oxidation.
Further, according to the present invention, preferably, each of the terminals has a stopper portion for engaging with the electrically insulating member.
According to the present invention, a stopper portion for engaging with the electrically insulating member is formed in each of the terminals. Thus, it is possible to improve the fixation strength of the terminals to the electrically insulating member.
Further, according to the present invention, preferably, the electroacoustic transducer further has a coil bobbin for holding the coil, and the coil bobbin is molded integrally with the electrically insulating member.
According to the present invention, the coil bobbin and the electrically insulating member are molded integrally by injection molding or the like. Thus, it is not necessary to bond the coil bobbin. It is therefore possible to improve the fixation strength of the coil bobbin to the electrically insulating member and it is possible to reduce the number of parts and the manufacturing cost.